{ config, lib, pkgs, ...}:

with lib;

let
  cfg = config.services.znc;

  defaultUser = "znc"; # Default user to own process.

  # Default user and pass:
  # un=znc
  # pw=nixospass

  defaultUserName = "znc";
  defaultPassBlock = "
        <Pass password>
                Method = sha256
                Hash = e2ce303c7ea75c571d80d8540a8699b46535be6a085be3414947d638e48d9e93
                Salt = l5Xryew4g*!oa(ECfX2o
        </Pass>
  ";

  modules = pkgs.buildEnv {
    name = "znc-modules";
    paths = cfg.modulePackages;
  };

  confOptions = { ... }: {
    options = {
      modules = mkOption {
        type = types.listOf types.string;
        default = [ "partyline" "webadmin" "adminlog" "log" ];
        example = [ "partyline" "webadmin" "adminlog" "log" ];
        description = ''
          A list of modules to include in the `znc.conf` file.
        '';
      };

      userModules = mkOption {
        type = types.listOf types.string;
        default = [ ];
        example = [ "fish" "push" ];
        description = ''
          A list of user modules to include in the `znc.conf` file.
        '';
      };

      userName = mkOption {
        default = defaultUserName;
        example = "johntron";
        type = types.string;
        description = ''
          The user name to use when generating the `znc.conf` file.
          This is the user name used by the user logging into the ZNC web admin. 
        '';
      };

      nick = mkOption {
        default = "znc-user";
        example = "john";
        type = types.string;
        description = ''
          The IRC nick to use when generating the `znc.conf` file.
        '';
      };

      passBlock = mkOption {
        default = defaultPassBlock;
        example = "Must be the block generated by the `znc --makepass` command.";
        type = types.string;
        description = ''
          The pass block to use when generating the `znc.conf` file.
          This is the password used by the user logging into the ZNC web admin.
          This is the block generated by the `znc --makepass` command.
          !!! If not specified, please change this after starting the service. !!!
        '';
      };

      port = mkOption {
        default = 5000;
        example = 5000;
        type = types.int;
        description = ''
          Specifies the port on which to listen.
        '';
      };
 
      useSSL = mkOption {
        default = true;
        example = true;
        type = types.bool;
        description = ''
          Indicates whether the ZNC server should use SSL when listening on the specified port.
        '';
      };

      extraZncConf = mkOption {
        default = "";
        type = types.lines;
        description = ''
          Extra config to `znc.conf` file
        '';
      };
    };
  };

  # Keep znc.conf in nix store, then symlink or copy into `dataDir`, depending on `mutable`.
  mkZncConf = confOpts: ''
    // Also check http://en.znc.in/wiki/Configuration
    
    AnonIPLimit = 10
    ConnectDelay = 5
    # Add `LoadModule = x` for each module...
    ${concatMapStrings (n: "LoadModule = ${n}\n") confOpts.modules}
    MaxBufferSize = 500
    ProtectWebSessions = true
    SSLCertFile = ${cfg.dataDir}/znc.pem
    ServerThrottle = 30
    Skin = dark-clouds
    StatusPrefix = *
    Version = 1.2

    <Listener listener0>
            AllowIRC = true
            AllowWeb = true
            IPv4 = true
            IPv6 = false
            Port = ${if confOpts.useSSL then "+" else ""}${toString confOpts.port}
            SSL = ${if confOpts.useSSL then "true" else "false"}
    </Listener>
    
    <User ${confOpts.userName}>
            Admin = true
            Allow = *
            AltNick = ${confOpts.nick}_
            AppendTimestamp = false
            AutoClearChanBuffer = false
            Buffer = 150
            ChanModes = +stn
            DenyLoadMod = false
            DenySetBindHost = false
            Ident = ident
            JoinTries = 10
            MaxJoins = 0
            MaxNetworks = 1
            MultiClients = true
            Nick = ${confOpts.nick}
            PrependTimestamp = true
            QuitMsg = Quit
            RealName = ${confOpts.nick}
            TimestampFormat = [%H:%M:%S]
            ${concatMapStrings (n: "LoadModule = ${n}\n") confOpts.userModules}
            
            ${confOpts.passBlock}
    </User>
    ${confOpts.extraZncConf}
  '';

  zncConfFile = pkgs.writeTextFile {
    name = "znc.conf";
    text = if cfg.zncConf != ""
      then cfg.zncConf
      else mkZncConf cfg.confOptions;
  };

in

{

  ###### Interface

  options = {
    services.znc = {
      enable = mkOption {
        default = false;
        example = true;
        type = types.bool;
        description = ''
          Enable a ZNC service for a user.
        '';
      };

      user = mkOption {
        default = "znc";
        example = "john";
        type = types.string;
        description = ''
          The name of an existing user account to use to own the ZNC server process.
          If not specified, a default user will be created to own the process.
        '';
      };

      dataDir = mkOption {
        default = "/var/lib/znc/";
        example = "/home/john/.znc/";
        type = types.path;
        description = ''
          The data directory. Used for configuration files and modules.
        '';
      };

      zncConf = mkOption {
        default = "";
        example = "See: http://wiki.znc.in/Configuration";
        type = types.lines;
        description = ''
          The contents of the `znc.conf` file to use when creating it.
          If specified, `confOptions` will be ignored, and this value, as-is, will be used.
          If left empty, a conf file with default values will be used.
          Recommended to generate with `znc --makeconf` command.
        '';
      };

      confOptions = mkOption {
        default = {};
        example = {
          modules = [ "log" ];
          userName = "john";
          nick = "johntron";
        };
        type = types.optionSet;
        description = ''
          Values to use when creating a `znc.conf` file.
        '';
        options = confOptions; 
      };

      modulePackages = mkOption {
        type = types.listOf types.package;
        default = [ ];
        example = [ pkgs.zncModules.fish pkgs.zncModules.push ];
        description = ''
          A list of global znc module packages to add to znc.
        '';
      };
 
      mutable = mkOption {
        default = false;
        example = true;
        type = types.bool;
        description = ''
          Indicates whether to allow the contents of the `dataDir` directory to be changed
          by the user at run-time.
          If true, modifications to the ZNC configuration after its initial creation are not 
            overwritten by a NixOS system rebuild.
          If false, the ZNC configuration is rebuilt by every system rebuild.
          If the user wants to manage the ZNC service using the web admin interface, this value
            should be set to true.
        '';
      };
 
      extraFlags = mkOption {
        default = [ ];
        example = [ "--debug" ];
        type = types.listOf types.str;
        description = ''
          Extra flags to use when executing znc command.
        '';
      };
    };
  };


  ###### Implementation

  config = mkIf cfg.enable {

    systemd.services.znc = {
      description = "ZNC Server";
      wantedBy = [ "multi-user.target" ];
      after = [ "network.service" ];
      serviceConfig = {
        User = cfg.user;
        Restart = "always";
        ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
        ExecStop   = "${pkgs.coreutils}/bin/kill -INT $MAINPID";
      };
      preStart = ''
        ${pkgs.coreutils}/bin/mkdir -p ${cfg.dataDir}/configs

        # If mutable, regenerate conf file every time.
        ${optionalString (!cfg.mutable) ''
          ${pkgs.coreutils}/echo "znc is set to be system-managed. Now deleting old znc.conf file to be regenerated."
          ${pkgs.coreutils}/rm -f ${cfg.dataDir}/configs/znc.conf
        ''}

        # Ensure essential files exist.
        if [[ ! -f ${cfg.dataDir}/configs/znc.conf ]]; then
          ${pkgs.coreutils}/bin/echo "No znc.conf file found in ${cfg.dataDir}. Creating one now."
          ${if (!cfg.mutable)
            then "${pkgs.coreutils}/bin/ln --force -s ${zncConfFile} ${cfg.dataDir}/.znc/configs/znc.conf"
            else ''
              ${pkgs.coreutils}/bin/cp --no-clobber ${zncConfFile} ${cfg.dataDir}/configs/znc.conf
              ${pkgs.coreutils}/bin/chmod u+rw ${cfg.dataDir}/configs/znc.conf
              ${pkgs.coreutils}/bin/chown ${cfg.user} ${cfg.dataDir}/configs/znc.conf
            ''}
        fi

        if [[ ! -f ${cfg.dataDir}/znc.pem ]]; then
          ${pkgs.coreutils}/bin/echo "No znc.pem file found in ${cfg.dataDir}. Creating one now."
          ${pkgs.znc}/bin/znc --makepem --datadir ${cfg.dataDir} 
        fi

        # Symlink modules
        rm ${cfg.dataDir}/modules || true
        ln -fs ${modules}/lib/znc ${cfg.dataDir}/modules
      '';
      script = "${pkgs.znc}/bin/znc --foreground --datadir ${cfg.dataDir} ${toString cfg.extraFlags}";
    };

    users.extraUsers = optional (cfg.user == defaultUser)
      { name = defaultUser;
        description = "ZNC server daemon owner";
        group = defaultUser;
        uid = config.ids.uids.znc;
        home = cfg.dataDir;
        createHome = true;
        createUser = true;
      };
 
    users.extraGroups = optional (cfg.user == defaultUser)
      { name = defaultUser;
        gid = config.ids.gids.znc;
        members = [ defaultUser ];
      };

  };
}